LESSON 11: Chromosome Mapping

If you have made it this far you are no longer a beginner! Chromosome Mapping is for the serious genetic genealogist. It can be time consuming, but also very rewarding. Since writing this back in 2011 there are many new tools to make it easier. Chromosome mapping is the only way to truly know that a segment of DNA comes from an identified ancestor or ancestor pair. It is the process genetic genealogists use to track matches and then confirm our matches’ relationship to us. You may need to collect quite a bit of data before using the mapping tools. Ancestry’s Common Ancestor and ThruLines and My Heritage’s Theory of relativity are attempts to automatic the process. As is MyHeritage’s Auto Clusters.

In our previous lessons you have already seen chromosome maps. Chromosome maps are simply graphic representations of shared DNA on an illustration of our chromosomes. The data used to illustrate or paint the maps is available by download from all companies except ANCESTRY. Those who have only tested at ANCESTRY you will need to upload to FTDNA, MyHeritage or GEDMATCH to be able to map matching segments. The cost to upload to all three is FREE, however a nominal fee may be charged to unlock all tools. (Currently a one time fee of $19 at FTDNA, $29 at MyHeritage. GEDMATCH has subscriptions to use higher level tools, but the basic tools are FEWW) If you have a match at ANCESTRY that is not in one of the other databases you will need to write and see if you can convince them to upload elsewhere.

Most serious genetic genealogists have been begging ANCESTRY for years for a chromosome browser. To date ANCESTRY has been steadfast in its opposition, ostensibly on the grounds of privacy. If they ever add matching segment information (by chromosome) and/or a Chromosome Browser they would blow the competition out of the water. Until then we must work around this obstacle the best we can.

At the time I originally wrote this Lesson my distant cousin Kitty Munson Cooper wrote a program at my request that allowed individuals to “paint their matches”. I have provided links at the bottom of the page. I used it for many years but have moved to using an easier tool called DNA Painter. Not only does this site provide opportunities to paint your chromosomes it gives you tools for predicted possible relationships, for instance what if the most likely and tools for creating beautiful trees. The basic website is FREE but if you want to use it more extensively there are options to do more at $5 per month.

What DNA Painter does is allows you to store matches, place them on the proper segments and chromosomes and assign them to various parts of your tree. You can do this in batches or individually. On the example below I have painted 72% of the chromosome with 828 segments. These are only painted for when I know the “likely” line on which we are related. The Light green splotches are where I cannot identify whether the match is paternal or maternal.

You paint a match by entering data from 23andMe, FTDNA, MyHeritage of GEDMATCH into the Paint a Match Field. Then you assign a category. You get to choose the category and the color used. I use warm colors for my Mother’s side and cool colors for my Father’s side. You can also change the segment size to include. For instance you might download a match at FTDNA and want to exclude segments under a given threshold like 5 or 7 cM. (FTDNA includes very small segments).

This is a closer look at my Key for the categories I have.

You can see I have included categories for Unknown Paternal, Unknown Maternal and Pending and unknown. Individuals with more than one spouse offer the opportunity to assign the match to a specif individual when you match someone who is the descendant of a different spouse (1/2 cousin). If you are serious about “proving” your matches, I highly recommend using DNAPainter.

You can periodically download your matches from FTDNA, 23andme and MyHeritage and organize them in your own spreadsheet or use the tools that that DNAGEDCOM make available. There is a Registration and cost involved but you may find this worthwhile. I used to keep a spreadsheet but now keep my matches in DNAPainter.